1. Field of Invention
The present invention relates to the collection and measurement of natural materials, contaminants, and polluting substances that accumulate in aquatic environments such as lakes, reservoirs, oceans, estuaries, and other bodies of water, and, more particularly, to apparatus positioned within bodies of water to automatically collect such materials and substances for the purpose of determining composition, rates of movement, and the general condition of water bodies.
2. Description of Prior Art
Devices referred to generally as time-series sediment traps have found widespread application in measuring the abundance of lacustrine and marine organisms such as bacteria, algae, other phytoplankton, and zooplankton. Such trapping devices have also been employed to determine the volume and flux of suspended particles such as silt, clay, and fragments of organic matter and various contaminants and polluting substances contained within or adhering to such particles. In addition, time-series sediment traps have been used to determine the point sources of natural and introduced particles as well as the time when such materials reached the location of a deployed device. Also, time-series sediment traps have been used in a wide range of scientific investigations such as the Joint Global Ocean Flux Study, an international global program to measure the flux of particles to the sea floor. Such investigations are an essential aspect of estimating the global cycling of carbon, which is related to environmental problems such as global warming. Other scientific investigations are concerned with particle movement during storms, tsunamis, and submarine landslides. Over the last three decades such devices have become a standard tool for investigating specific aquatic events, tracing pathways of pollution, and monitoring changing conditions in lakes, oceans, and estuaries.
Time-series sediment traps employ a cone or funnel to greatly magnify the volume of material that settles in collecting chambers and they also provide a means for collecting materials at regular time intervals. One such time-series device, developed by the present inventor, collected materials in a single, long collecting tube and marked the time intervals by periodically dropping plastic granules into the collecting tube. The present inventor was granted a utility patent for this device in 1973 by the U.S. Patent Office (U.S. Pat. No. 3,715,913, now in the public domain). This device was used in various investigations by research scientists, environmental contractors, and government agencies. Although the simple device provided by U.S. Pat. No. 3,715,913 was effective in certain situations, a failure of the marking system to isolate settled materials under some common conditions restricted its use to a limited number of applications. The problem is traceable to the granules of TEFLON® that were employed to mark time intervals. For example, if settled materials had a high fluid content, the granules settled differentially to form a poorly defined marking layer. If rates of accumulation were low, two or more marking layers were indistinguishable. A slight and often unavoidable tilting of the collecting tube after deployment resulted in the streaming of granules down one side of the collecting tube, resulting in failure to identify a time-marked interval. Upon recovery of the collecting tube uncertain boundaries between layers of granules limited the accuracy of sampling. In addition, granules required removal from a sample before measuring the volume and weight of recovered materials, but other materials were removed also, distorting the measurements of volume and bulk density.
The above-cited problems of an automated method for collecting aquatic materials in a single collecting tube by periodically releasing granules from a dispensing device limited the use of the method and favored a trap design in which materials are collected in individual bottles that are automatically and sequentially rotated below the narrow open end of a funnel. Although most time-series trap investigations now collect samples in many separate wide-mouth bottles or cups, this currently favored method has serious limitations. Among problems of collecting materials in multiple bottles is a failure to provide uninterrupted and undisturbed records of sediment accumulation. Continuous records of events talking place in water bodies are highly desirable because many such events are short-lived and are accompanied by abrupt changes in color, texture and composition of materials. For example, the effects of storm events, by flushing coarse particles from stream channels and by re-suspending already accumulated bottom sediments are well known, and are accompanied by changes in the physical and chemical properties of materials collected in funnel-shaped traps. Indeed, these same textural and composition changes in the water bodies are magnified in cone-shaped traps and clearly revealed in single, elongate collecting tubes. In another example, sewage outfall after heavy rains often contains contaminating substances that are confined to a “spike” and are thereafter dissipated. However, the current practice of collecting such evidence in many wide-mouth bottles or cups, and the unavoidable disturbance of collected materials during recovery fails to preserve evidence for such short-lived events. A single rotated vessel, for example, commonly collects material in 30-day intervals. But a single event such as a pollution episode may occur both before and after vessels are exchanged, thereby providing only a 60-day resolution for an event that occurred within one or a few days.
All of the problems and limitations of currently deployed, funnel-shaped, multiple-vessel, sediment trapping devices, with respect to loss of continuity and preservation of structures, textures, and composition are overcome by providing an innovative and major improvement in the method of isolating aquatic materials collected in an elongate vessel. Not only does the present invention replace the need for collecting samples in many rotated vessels, it overcomes all of the problems specific to such vessels, as well as all of the problems and disadvantages previously encountered with devices that mark regular time intervals in a single, elongate collecting tube.